A. Field of the Invention
The present invention relates to hitch assemblies for connecting a trailer to a towing vehicle. In addition to interconnecting the trailer and the towing vehicle, the towing apparatus or hitch assemblies support the front end of the trailer. The novel towing apparatus disclosed herein incorporates a wheel or set of wheels which can bear part of the trailer's weight, as well as features adapted to dampen forces on the connection between the trailer and the towing vehicle, and is particularly useful for towing large trailers containing heavy loads.
Trailers are generally connected to trailer hitches which are mounted either to the bumper of a towing vehicle or, in the case of large trailers, to the towing vehicle's frame. A typical trailer has a forwardly-extending element called the trailer tongue. The vehicle trailer hitch is adapted to mate with a latching component which is mounted either on the trailer tongue or on a drawbar connecting the hitch to the trailer tongue.
Ideally, a trailer would incorporate two or more axles, spaced widely apart, which would support the mass of the trailer, and any cargo. Such is the case when a car is towed by another vehicle equipped with a two bar. The car's two axles support the mass of the car, while its freely steerable front axle turns the car with the towing vehicle. Similarly, for trailers with widely spaced apart multiple axles, the front axle must be either freely steerable, or coupled to the towing vehicle's steering system. However, both alternatives are impractical in most cases. As a result, a typical trailer contains either a single axle, or multiple axles mounted in close proximity.
If the trailer axle or axles are mounted adjacent the rear of the trailer, the distance between the trailer axle(s) and the trailer hitch is relatively large, producing a large load on the rear axle of the towing vehicle. As a consequence, a towing vehicle may have sufficient horsepower to pull a heavy load in a trailer of this type, but will be unable to support the large mass bearing down on towing vehicle's rear axle. To counteract this problem, some trailer manufacturers place the axle(s) near the center of the trailer. However, this requires a careful balancing of the initial load in the trailer, and a constant re-balancing as items are removed from and added to the trailer. Moreover, a center-axle trailer which has been designed to carry a certain load (for example, a single heavy object) may be unsuitable for other purposes.
Placing the axle of a trailer near the trailer's center causes another problem. As a trailer is being towed, it will bounce and pitch forward and back due to imperfections and changes in the road. Any such motion of the trailer will be transmitted to the towing vehicle, and a corresponding load transferred to the trailer hitch. With the trailer's center of gravity near a pivot point (the axle), the pitching motion can become severe, causing excessive loading of the hitch, excessive wear of the hitch ball, and an uncomfortable (and potentially dangerous) ride in the towing vehicle.
B. Related Prior Art
The problem of counteracting the forces generated by a towed trailer has been recognized in the art. For example, Hensley U.S. Pat. No. 5,660,409 is directed to a trailer hitch assembly which is adapted to limit swaying (fishtailing) by incorporating a link mechanism which dampens sideways movement. Lewis U.S. Pat. No. 3,756,618 employs pistons which connect the trailer tongue to lever arms in order to dampen sideways movement. However, neither of these references suggests a solution to the problem of handling excessive weight on the trailer hitch.
U.S. Pat. Nos. 5,785,330 and 5,823,558, both to Shoquist, are also of interest to the background of the present invention. Both patents are directed to apparatus for relieving the load imposed on the hitch of a towing vehicle by providing adjustable wheel assemblies to handle a portion of the weight of the trailer which would otherwise bear on the towing vehicle's rear axle. In both Shoquist patents, the wheel assemblies are supported by a superstructure which is mounted to a rigid trailer frame. The superstructures contain sleeves which serve as spindle mounts for a vertically-extending spindle to which wheels are attached. The spindles are equipped with either compression springs or air-bag pistons to dampen up and down movement of the trailer during towing.
The apparatus disclosed in the Shoquist '330 patent incorporates steering dampers in the form of hydraulic cylinders to control the turning motion of the wheel assembly when the trailer is turning. In one embodiment illustrated in the Shoquist '558 patent, the wheel assembly is adapted to be manually retractable in order to facilitate movement of the trailer in reverse.
Both Shoquist patents disclose features for adjusting the relationship between the spindle-holding superstructure and the trailer frame to accommodate the particular size and weight of the trailer and its load. Once this adjustment is made, the superstructure and the trailer frame are bolted together to form a rigid structure, locking the wheel in place. In addition to bearing the weight of the trailer's front end, the spring or air-biased Shoquist wheel assemblies function to dampen some of the up-and-down movement of the trailer with respect to the towing vehicle.
One limitation of the Shoquist designs is that the wheel assemblies only accommodate a portion of the static load bearing down on the towing vehicle. Shoquist's springs are set to support a certain amount of load, with the remainder being supported by the towing vehicle's hitch. The spring must be re-set every time the cargo in the trailer changes.
During actual operating conditions, while the trailer is pitching forward and back, a dynamic load is introduced. When the trailer is pitching forward, the trailer tongue will bear down harder on the tow vehicle, causing the spring to push up harder and absorb some of the additional load. When the reverse occurs, the trailer tongue tends to pull up on the hitch ball. The wheel assembly spindle spring is also pushing up on the tongue. These two forces are additive, so that upward force on the trailer hitch will actually increase during the upwards cycle. Because hitch/ball assemblies utilized to couple trailers to towing vehicles are primarily designed to support downward loads, this result is not desirable.
Similar problems occur while driving over a raised center median, a speed bump, an entrance ramp to a gas station, or other similar obstacles. The wheel assemblies employed in the Shoquist devices will pass over such an obstacle and be pushed up while the rear of the towing vehicle is dropping down over the other side of the obstacle. Again, the result is the spindle spring adding to the upward force generated by the trailer pitching back while the rear of the towing vehicle is trying to move downward. In the extreme (as in the case where most of the travel in the spring has been taken up to accommodate a particularly heavy trailer), the wheel assembly may not have enough travel to clear the obstacle. This creates a situation where the entire weight of the trailer can be cantilevered off of the trailer tongue. As a consequence, the towing assemblies depicted in the '330 and '558 patents do not provide a total solution to the trailer-towing problem.